SOLUTION: A farmer has 1000 feet of fence. He wants to enclose a pasture bordering on long straight river where no fence is needed. Find the area of the largest such enclosure. Thank

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Question 255888: A farmer has 1000 feet of fence. He wants to enclose a pasture bordering on long straight river where no fence is needed. Find the area of the largest such enclosure.
Thank you for help.

Answer by drk(1908) About Me  (Show Source):
You can put this solution on YOUR website!
We have two formulas:
(i) P+=+2x+%2B+y, where p =1000. Note we only have 3 sides.
(ii) A+=+xy
From (i) we get
(iii) 1000+=+2x+%2B+y
Solve (iii) for y to get
(iv) y+=+1000-2x
substitute (iv) into (ii) to get
(v) A+=+x%281000-2x%29
which is
(vi) A+=+-2x%5E2+%2B+1000x
set -2x^2 + 1000x = 0 and create vertex form as
%28x-250%29%5E2+%2B+125000
so the max area is 125,000 sq. ft.